Eukaryotes And Prokaryotes

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Microorganism Types Plantae and Animalia Protists Eukaryotes and Prokaryotes Primary Subdivisions of Cellular Organisms Monera Main Groups of Microorganisms Bacteria Actinomycetes Protozoa Algae Fungi Viruses Microbial Classification Approaches Artificial Approach Natural Approach

Eukaryotes And Prokaryotes

	Eukaryotes And Prokaryotes - The development of electron microscope and some other techniques in 1950 could provide details of fine structure of cells. Within few years, there were revealed some hitherto unknown interesting features of cell ultrastructure. This led to a fundamental dichotomy among the various groups of organisms with respect to the internal architecture of the cell: two radically different kinds of cells exist in the contemporary living world: (1) the more complex eukaryotic cell is the unit of structure in plants, metazoan animals, protozoa, fungi and algae, and
(2) the less complex prokaryotic cell is the unit of structure in two microbial groups: bacteria and cyanobacteria or blue green bacteria (formerly known as blue green algae). The microorganisms thus belong to both these groups. Thus algae, fungi and protozoa are eukaryotes and all bacteria including cyanobacteria are prokaryotes. Some authors call the eukaryotic microbes as higher protists and prokaryotic microbes as lower protists.
If, the term protists is still to be retained at all, this has been restricted to the eukaryotic microbes i.e. algae, fungi and protozoa just to distinguish them from the Plantae and Animalia. We shall describe the detailed organisation of prokaryotic and eukaryotic cells later. However, the chief points of differences between the two will be briefly indicated here. The eukaryotic cells contain a nucleus with a nuclear membrane, multiple chromosomes and a mitotic apparatus to ensure equal partition of the products of chromosomal replication to the two daughter cells.
The nucleus of a prokaryotic cell is a single, circular chromosome, without a nuclear membrane and without histones. Prokaryotic cells also lack membrane bound organelles (mitochondria, lysosomes). There is no endocytosis and intra cellular digestive vacuoles. They lack (with few exceptions) steroids.
	They have unique components (muramate and often diaminopimelate) in cell walls. Some prokaryotes are able to fix atmospheric nitrogen and carry obligate anaerobiosis. Some major differences between prokaryotes and eukaryotes. Thus with respect to the internal architecture of the cell, the more complex is the eukaryotic cell, which is the unit of structure in plants, metazoan animals, protozoa, fungi and algae. The less complex is the prokaryotic cell, the unit structure of two microbial groups: the eubacteria (including the cyanobacteria, formerly known as blue green algae) and the archaebacteria, a heterogeneous group of microbes with prokaryotic structure but with a cell chemistry that is strikingly different from that of the eubacteria.

The differences between archaebacteria and eubacteria are so profound that most now believe that this distinction reflects an evolutionary divergence as fundamental as that which divides the eukaryotes from either of the two groups of bacteria.

These newly recognised lines of demarcation run through Haeckels proposed kingdom of Protists. Protozoa, fungi and algae (with the exception of blue green algae) are eukaryotes which share with plants and animals a common cell structure (eukaryotic) and many details of cell chemistry and function.

The eubacteria include most bacterial groups (including the cyanobacteria). The archaebacteria include only three known groups indistinguishable from the eubacteria on structural grounds but profoundly different chemically. In future, more groups of archaebacteria could be recognised.

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Phylogenetic Approach Adansonian Approach - Numerical Taxonomy Macromolecular Approach DNA Base Composition DNA Base Compositions of Representative Bacteria Constancy of G+C content in Strains of Bacteria Nucleic Acid Hybridization Classification of Bacteria from Bergey's Manual of Determinative Bacteriology

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